On Sun, Nov 17, 2024 at 12:49:46PM +0100, Peter Zijlstra wrote: > On Tue, Nov 05, 2024 at 02:33:54PM +0100, Jiri Olsa wrote: > > hi, > > this patchset adds support to optimize usdt probes on top of 5-byte > > nop instruction. > > > > The generic approach (optimize all uprobes) is hard due to emulating > > possible multiple original instructions and its related issues. The > > usdt case, which stores 5-byte nop seems much easier, so starting > > with that. > > > > The basic idea is to replace breakpoint exception with syscall which > > is faster on x86_64. For more details please see changelog of patch 7. > > So this is really about the fact that syscalls are faster than traps on > x86_64? Is there something similar on ARM64, or are they roughly the > same speed there? yes, I recall somebody was porting uretprobe syscall to arm, but there was no speed up IIRC, so looks like it's not the case on arm I can't find the post atm, I'll keep digging jirka > > That is, I don't think this scheme will work for the various RISC > architectures, given their very limited immediate range turns a typical > call into a multi-instruction trainwreck real quick. > > Now, that isn't a problem if their exceptions and syscalls are of equal > speed.
